This application relies for priority upon Korean Patent Application No. 2001-18212, filed on Apr. 6, 2001, the contents of which are herein incorporated by reference in their entirety.
1. Field of the Invention
The present invention generally relates to a display apparatus, and more particularly to a display apparatus with improved sensing speed of resolution change and sensing method thereof.
2. Description of the Related Art
Cathode-ray tube (CRT) display apparatus produces images on a screen by generating electron beam which strikes a phosphorescent surface of the screen. An electric gun installed in a rear portion of the apparatus generates the beam of electrons, which are deflected by horizontal and vertical polarization coils for alternating the direction of the beam. The screen displays the images when portions of the screen are struck by the electron beam. The CRT display apparatus displays characters and images on screen, and it is commonly utilized as a computer output device.
The electron beam is scanned periodically in accordance with a period of sawtooth current of a deflecting yoke, but the period should be synchronized with a scanning period required for a host. Synchronization is achieved by a synchronization signal sent from the host. The synchronization signal is divided into a horizontal synchronization signal controlling a horizontal scanning period, and a vertical synchronization signal controlling a vertical scanning period.
Meanwhile, the resolution change in the CRT display apparatus is achieved by the frequency change of the horizontal and vertical synchronization signals provided from the host. For instance, for the video graphic array (VGA) representing 640xc3x97480 pixels, the frequency of horizontal synchronization signal is 30 KHz and the frequency of the vertical synchronization signal is 60 Hz. For super VGA (SVGA) representing 1024xc3x97768 pixels, the frequency of horizontal synchronization signal is 35-37 KHz and the frequency of the vertical synchronization signal is 70 Hz.
The resolution change in the CRT display apparatus is achieved by the frequency change of the horizontal and vertical synchronization signals provided from the host. The conventional CRT display apparatus senses the resolution change by detecting one period of the vertical synchronization signal, and calculates the number of pulses of the horizontal synchronization signal provided from the host during the detected period of the vertical synchronization signal.
However, if the resolution of the display apparatus is changed, e.g., from VGA to SVGA, or from SVGA to VGA, component circuits for the CRT display apparatus are often damaged due to the sudden operating frequency change, and a large amount of time is required for sensing the resolution change.
A display apparatus displaying a picture signal synchronized with a synchronization signal provided from a host is provided, wherein the display apparatus includes: a counting circuit for counting a first number of pulses of the synchronization signal provided from the host, and generating a counted number of pulses in a predetermined time period; a register for storing the first number of the pulses provided from the counting circuit; and a comparator for comparing a second number of pulses newly provided from the counting circuit with the first number of pulses stored in the register, and generating a resolution change sensing signal when the first number of pulses and the second number of pulses are different. Preferably, the counting circuit includes: a counter for counting the number of pulses of the synchronization signal; a timer for generating a control signal every predetermine time period; and a switching circuit transferring the counted number of pulses to an output in response to the control signal.
According to an aspect of the invention, the timer generates the control signal every 1 millisecond, and the synchronization signal is a horizontal synchronization signal.
A display apparatus for displaying a picture signal synchronized with a composite signal of a horizontal synchronization signal and a vertical synchronization signal is also provided which comprises: a synchronization signal separator for dividing the composite signal into the horizontal synchronization signal and the vertical synchronization signal; a counting circuit for counting a first number of pulses of the horizontal synchronization signal separated from the synchronization signal separator, and generating a counted number of pulses in a predetermined time period; a register for storing the first number of pulses provided from the counting circuit; and a comparator for comparing a second number of pulses newly provided from the counting circuit with the first number of pulses stored in the register, and generating a resolution change sensing signal when the first number of pulses and the second number of pulses are different.
According to a preferred embodiment of the present invention, the horizontal synchronization signal separated from the synchronization signal separator is same as the composite signal.
The synchronization signal separator includes an up/down counter performing an up-count when the composite signal is a first level, and performing a down-count when the composite signal is a second level, and an overflow signal provided from the up/down counter is the vertical synchronization signal.
The counting circuit includes: a counter counting the number of pulses of the horizontal synchronization signal separated from the synchronization signal separator, and generating the counted number of pulses; a timer generating a control signal in a predetermined time period; and a switching circuit transferring the counted number of pulses from the counter to an output in response to the control signal, wherein the counter is reset by the control signal provided from the timer. The timer generates the control signal every 1 millisecond.
According to a preferred embodiment of the present invention, the display apparatus further includes a flag register being set during an activating period of the vertical synchronization signal separated from the synchronization signal separator, wherein the comparator performs a frequency correction for the vertical synchronization signal included in the horizontal synchronization signal when the flag register is set. A method for sensing resolution change in a display apparatus displaying a picture signal synchronized with a synchronization signal provided from a host is provided, wherein the steps include: generating a first counted number of pulses in a first predetermined time period by counting a first number of pulses of the synchronization signal from the host; generating a second counted number of pulses in a second predetermined time period by counting a second number of pulses of the synchronization signal from the host; comparing the first counted number of pulses and the second counted number of pulses; and generating a resolution change sensing signal when the first counted number of pulses and the second counted number of pulses are different.